This invention relates in general to ball nut and screw mechanisms and in particular to an improved structure for a load lock adapted for use with such a ball nut and screw mechanism.
The ball nut and screw mechanism is a well known device which is adapted to translate rotary motion into linear motion. Such a mechanism typically includes an elongated cylindrical screw which extends through a cylindrical opening formed through a nut. The outer surface of the screw and the inner surface of the nut are formed having complementary helical threads which are generally semi-circular in cross section. However, the outer diameter of the screw is smaller than the inner diameter of the opening formed through the nut. Thus, the outer surface of the screw and the inner surface of the opening formed through the nut do not engage one another. Rather, a plurality of balls are disposed between the screw and the nut. Each ball extends partially into both of the complementary threads formed in the screw and the nut so as to provide a rolling engagement therebetween, similar to a ball bearing.
Typically, the screw is connected to a source of rotational power, while the nut is secured so as to be non-rotatable. Thus, when the screw is rotated, the nut is moved linearly relative thereto. In some instances, however, the nut is fixed to be stationary, and the screw is moved axially as it rotates. In either event, because of the rolling engagement of the balls with the screw and the nut, such linear movement of the nut or screw is accomplished with very little friction. However, as the screw is rotated, the balls roll throughout the threads formed in the nut. To accommodate this, it is known to provide a means for permitting the balls to circulate from one end of the nut to another in an endless loop. This ball circulation means typically includes a pair of apertures formed through the nut and an external tube extending between the apertures. The apertures extend radially through the nut into communication with the ends of the threads formed therein. The tube has end portions which extend into the apertures. The tips of the end portions of the tube may be formed having integral deflectors which guide the balls into and out of the threads. Thus, when the screw is rotated, the balls roll through the threads toward one end thereof, into one end portion of the tube disposed in one of the apertures, through the tube, out of the other end portion of the tube disposed in the other one of the apertures, and into the other end of the threads.
So long as the balls are retained between the nut and the screw, the ball screw and nut mechanism will function normally. However, it is known that the mechanism can fail if the balls are removed from between the screw and the nut. Most frequently, this occurs when the external ball circulation passageway is accidentally damaged or removed, allowing the balls to fall out of the mechanism. When this happens, the screw and the nut may become free to move axially relative to one another. As a result, the mechanism becomes inoperable. Also, a load carried by the nut may undesirably become free to move suddenly and uncontrollably.
To prevent this from occurring, it is known to provide the ball screw and nut mechanism with a load lock which prevents the nut from moving axially relative to the screw when the balls are not present. Such a load lock is preferably designed such that it does not interfere with the normal operation of the mechanism, but rather only engages the screw and the nut only when the balls are not present in the threads. Many different load locks are commonly available for use in ball screw and nut mechanisms. However, known load locks are typically constructed from multiple components and, as a result, are rather expensive and time consuming to properly install. Thus, it would be desirable to provide an improved structure for a load lock for a ball screw and nut mechanism which is simple and inexpensive in construction and installation.